As a control system for an automatic transmission, a conventional technique is known as described for example in Japanese Patent No. 3870676. In this publication, occurrence of excessive engine braking force is suppressed by switching a target engine rotational speed depending on an engine load when an accelerator pedal is off and released. Specifically, the target engine speed is set at a high speed while the target engine speed is set at a low speed when a throttle opening is small.
However, if the above control is applied to a belt-type continuously variable transmission, when changing the target engine speed in an accelerator pedal off state, shifting of the belt type continuously variable transmission is performed. Then, a problem of vehicle vibration occurs when the shift speed is high due to hydraulic vibration.